In many power generating systems it may be advantageous from the viewpoints of various design and constructional aspects to connect a generator to a prime mover, e.g. a wind turbine, via a gear-box arranged to convert the rotational speed of the prime mover into a speed range suitable for the generator. Correspondingly, in many motor applications it may be advantageous to connect an electrical motor to an actuator via a gear box arranged to convert the rotational speed of the electrical motor into a speed range suitable for the actuator. The gear-box may comprise one or more series of connected gear stages with the aid of which a desired gear ratio is achieved. Each single gear stage can be, for example, a planet-gear stage or a cylindrical gear stage.
Challenging design aspects related to a combination of a gear-box and an electrical machine that can be a generator and/or a motor are, among others, the size and weight of the combination. Furthermore, equipment needed for lubricating, cooling, and monitoring the combination of the gear-box and the electrical machine may be complex compared with that of e.g. a gearless system. The reliability of e.g. the lubricating systems may require special attention because, as self-evident, both the lubricating system of the gear-box and the lubricating system of the electrical machine have to simultaneously work properly in order that the combination works properly. Therefore, for obtaining a sufficient effective or combined reliability, the reliabilities of the lubricating systems of the gear-box and of the electrical machine respectively have to be significantly higher than the reliability that would be required for a single lubricating system of a gearless system. However the gear-box, especially in many wind power applications, makes it possible to use an electrical machine that is significantly smaller in dimensions and weight than an electrical machine of a corresponding gearless system. Therefore, the choice whether to use a gear-box or to have a gearless system depends on many different aspects many of which are more or less in trade-off with each other. The gear-box provides many advantages and thus there is a need to provide technical solutions for alleviating or even eliminating the drawbacks related to the use of the gear-box.
In many special applications, such as in wind turbines for example, the size and weight of the combination of an electrical machine, such as a generator or an electrical motor, and a gear box is of a critical importance, since these features affect many other design aspects directly related to this combination. These include, among others, the support structure for the combination as well as required space for the combination.
Therefore, there is a great demand for smaller and lighter combinations of a gear-box and an electrical machine.
It should also be noted, that an electrical machine in the context of the present application may be a generator or an electrical motor.